Renewable electric fuse and method of making it



July 25, F N, ON NT RENEWABLE ELECTRIC FUSE AND METHOD OF MAKING IT Filed Oct. 31, 1928 cit Patented July 25, 1933 FltiHKLIN N.

CON'ANT, OF nnwn'o'nrron'r,

MASSACHUSETTS, ASSIGNOR TO THE CfeiASE-SHAWMUT COMPANY, OF NEXVBURYIOR'E, MASSACHUSETTS, A CORPORATION MAS$ACHUSETTS RENEWABLE ELECTRIC FUSE AND IVIETl-IOD OF MAKING IT Application filed. fictober 3 This invention relates to renewable cartridgo type electric fuses of both the knife blade and ferrule terminal type.

Arenewable cartridge type electric fuse 1:15 a tubular enclosing casing made of inulating material which, usually, is fibre. lhe insulating tube has screw threads at he ends and metal end caps or ferrules are removably screw-threaded thereon. The ma- .terial of which the tube is composed, shrinks and swells with variations in atmospheric conditions so that at some times the end caps are tight anu at some times the end caps are loose on the casing. A tight end cap is difiicult to remove and, if excessive force is applied may damage the fuse. A loose end cap may impair the interrupting capacity of the fuse since it can permit dangerously hot to be expelled from the casing when the fuse blows under heavy load. lVith continued use the threads on the fibre tube wear so that the end cap can not be screwed down tightly. In an attempt to overcome these difi iculties, the fibre tubes have been made with heavy screw-threaded metal members at the ends. This construction, however, is not satisfactory because the fibre tube shrinks away from firm engagement with the metal members, so that they are loose on the casing. The construction is also undesirable since the metal members must have thick walls and so the screw-threaded members either must be considerably larger in diameter tha Qthe diameter of the insulating tube, so that the metal end caps or ferrules must greatly exceed the diameter of the tube, or the fibre tube must have a thick wall and must be turned down at the ends to receive .10 the heavy screw-threaded members.

An objectof the present invention is the provision of a. cartridge type fuse having a tubular insulating casing that has screwthreaded end shells that are maintained in firm engagement with the insulating tube 50 thin screw threaded metal end ferrule that Serial No. 316,210.

is permanently in pressure engagement with the end of the insulating tube.

Another object of the invention is the provision of a renewable cartridge type fuse having a screw-threaded metal ferrule on the end of the enclosing casing and a removable fusible element therefor which is so arranged that it is held in the casing against rotation and also holds the screw-threaded ferrule against rotation.

further object is the provision 'of a renewable fuse having an end cap which the a screw-threaded engagement with the tubular insulating casing and wherein means are provided to relieve the casing threads from wear occasioned by the screwing on and off of the end cap.

A further object is generally to improve the construction and operation of removable cartridge type electric fuses.

Fig. 1 is a side elevation of the renewable cartridge type fuse embodying the present invention, with one of the end caps shown in section.

Fig. 2 is a sectional elevation of the fuse of s a view of the left hand end of e of ig. 1. l 15 a view of the right hand end of of Fig. 1.

1g. is a perspective view of the removable fusible element of the fuse.

Fig. 6 is a plan detail of the right hand knife blade terminal of Fig. 5, the discs carried by the knife blade being shown in section.

Figs. 7 through 13 are sectional details illustrating progressive steps in the manufacture of the insulating casing and its screw-threaded metal shell.

Fig. 14 is a sectional detail of a renewable electric fuse of the ferrule type embodying the invention.

Fig. 15 is an end view of the enclosing casing of Fig. 14-, with the ferrule and endwasher removed.

As here shown, the renewable cartridge type electric fuse embodying the invention comprises a tubular casing 10 composed of insulating material as fibre which is susceptible to variations in atmospheric conditions and which shrinks and swells accordingly. The casing is provided with screw-threaded metal shells or sheaths 12 at its end, con structed in a manner hereinafter to be described and metal end caps i l and 16 re spectively which are .crew-threaded on said shells and casing to hold the removable unit in place. The tubular casing and the met-a1 shells are made and united in such a manner that the shells are attached rigidly to the ends of the casing at all times and under all usual operating conditions of the fuse and preserve constant dimensions of the screwthreaded portions of the ferrules so that the end caps 14: and 16 fit thereon in the intended manner at all times.

In the manufacture of the fuse, the tubular casing 10 is first run through a die which compresses it and reduces it to a predetermined diameter. Screw-threads 18 are then cut or formed in the periphery of the tube near the ends, and the tube between the screw threads and the ends is turned down to the level of the base of the screw threads thus forming a reduced annular shoulder 20. The casing is then in condition to receive the metal shell. The metal shell or sheath is, at one of the first stages of manufacture thereof, a ferrule of thin ductile metal a indicated in Fig. 8 having a cylindrical or tubular wall 22 and an imperforate end wall 24. The next operation on the ferrule is to form the cylindrical wall 22 with an annular step or neck 26 of reduced diameter which is adapted to fit snugly on the annular shoulder 20 of the insulating casing. External screw threads 28 and corresponding complemental internal screw threads 29 are then formed, by rolling or otherwise, in the cylindrical wall 22; and the end wall 24 is provided with the axial opening 30 as shown in Fi 10. "he internal diameter of the screwthreaded portion of the ferrule is suca that it snugly fits the externally screw-threaded end of the casing and is applied thereto as shown in Fig. 11. If found desirable, the shell with the perforated end wall can be applied to the end of the casing and the screw-threads can be rolled therein to conform with the screw threads 28 of the casing. In any event, the construction of the shell and casing is such that the shell fits tightly on the casing. A tapered expanding tool A, Fig. 11, is then forced in the opening 30 in the end wall of the shell, thereby to force the end wall 24 inwardly of the tubular casing and to convert the wall to an annular flange and to compress the flange firmly and permanently against the inner face of the casing. In this manner the end of the casing is compressed oetaveen the inner and outer annular sections 26' and 2strespectively of the shell. and is held permanently in this relation and thus is prevented from shrinking and swelling. Consequently, the metal shell tightly grips and is held firmly on the end of the casing. -The annular section 26 of the shell is punched at various localities to provide spurs 32, Figs. 1 and 13, which are embedded in the annular section 20 of the casing and thus positively lock the shell against rotation. The metal wall 22 of the ferrule is so thin that it does not materially increase the diameter of the insulating casing thereat and also is so thin that the cap threads can mesh with the casing threads, as is clear from an inspection of Fig. l3, so tl'lat the casing threads hold the end cap from axial displacement on the casing and the metal ferrule takes the wear that otherwise would materially fall on the easily-worn casing threads. The casing at one end s provided with dianietri(tally-opposed notches S4: Yv'lllCll extend axially through the annular shoulder 20 of the casing and also through the inner and outer sections 24; and 28 of one of the shells. The functions of these slots is to hold the removable fuse unit in place against rotation.

The removable fuse unit for the fuse il lustrated in Figs. 1 and 2 consi ;s of an iir-udating bar 36 to the ends of watch knife blade terminals 38 and 40 are rigidly seem-ed. A fusible link 42 removably connected with the inner ends of the knife blade terminals by means including clamping screws 44;. The knife blade 40 is provided with means by which he removable unit is locked to the enclosing casing against rotation. To this end, the inner end alOa of the knife blade ter minal is made narrower than the outer end and discs 48, 50 and 52 are secured thereon between the shoulder 54 of the wide part of the knife blade terminal and projections 56 of the narrow part of the terminal. The disc 52 is adapted to be seated upon the right hand end of the enclosing casing and against the metal ferrule 12 thereon. The end cap 16 has an annular hole 58 in its end wall 60 in which the knife blade term nal is located and the end wall is adapted to bear against said disc 52 whereby to clamp it against the end of the casing and to secure the removable unit within the enclosing casing. The discs 48 and 50. are adapted to fit within the enclosing casing and to engage the inner face thereof whereby to hold the removable unit central! v within the casing. The disc 50 is provided with a pair of diametrically-opposcd outstanding lugs or projections 62 which are located within the slots 34 of the right hand end of the casing whereby to hold the removable unit against rotation. The lugs engage both the edges of the screw-threaded shell and the edges of the enclosing casing at said slots and thus positively lock the shell against rotation on the casing at the time the end cap 16 is turned. The discs 48 and 50 are provided with axially disposed grooves (34 g 15 compressed,

amet-er that aid screw threadaid casin b Iree from threads and sa dVlIlg an internal d1 arneter of s 'l casing. enewahle electric fuse of the carthe I which the end of s both flan er *ith of the L lSL me out hi ch re peripheries w coves 66 rined in the inner 11 extend to t their 1sc 52 and w said d1 d ery of ell, and extern t lesser ne end 0 ernal screw g the screw ell havlng an e end portion ion "edei-zed tien 0 d nor L-l011 a sort "i g, said s' reade o1't101 and t ic fuse of the e mgsgin .e aid r enclosing casing of rng one end, a thin ductile metal s ternal )utc '1 nurar i.

e eiectr screw threads,

rhula ted in ree l hrea as FL l e 4 el uterial hav cesi 1L also havinp' t L LL in? rol screw thre f said read-. diameter than the screw 11 said azn ing.

ne end, e at and enterr ewthe inne ore d disc '1 in and against ro- )ther 8 at the other s ah L s then scre' eel: the reino 211 713 type ren slain ith r the s end c rn 16 i on the shell to l.

use the shell at ted so i the slots red thereto he d can screwed 0n the meta ine with he casing.

111 the cssn The ot 20 threaded F f4 illnst-ra: able tns asseinhlin the t in 1 ft ed no the end cap.

has seen within 3'. he en casing and is l 15 111 is end 0 i sertcd I tended thre cap 1 5:.

unit in place.

a slot in H to E 8 under the outer fac ed eve net/alt te e the metal shell to co 4 .1. seto c s plac an a; the

inner ha v- 195 iced sa [d i ateria iic tric fuse, a tubular :atin ads and a redi end of the cashed in c0nnec- ID i tot

rise strip between it an I lamp the disc on e same as above descrl knife blade fuse.

tion with the screw threads and the end of said casing, em

(r 1 i '0 ds received 1 and haVi the irn corresnondin t lrea hel la: section recei ed crew threads of s and a thin re inc-ed thread on that is compressed 3 aid casing.

the s flan face of s e er i ler in diameter e screw-ton h ft 1. i a

of th ads and a reduced section between I well 11 and external screw hreads received on the screw threa 1' the end of end 0 annular ew threads and the 115 rolled interns section of said casing and hav ing; external screw thre thread-tree scr and a thin ductile metal sponel shell and having a reduced t nular engagethe inside a tubular aterial havin ds IQCQlVEd on nu g spaced s between part that is refiexed ov thin dnc 1 .L imenien Dal iavin Y atnig 1n thre screw threads and i said e side thereet.

lectric 1h insul threads :1

olled c0 inete= e and also on the OH:

vlngz; r ernal screw said casing internal and external annuear flange ing into the interior thereof and having within said casing an annular flange that is compressed against the inner face of said casing, said fuse having a notch in theend thereof which is located in tile end of said casin D and also in said annular flange.

7. A renewable electric fuse including the combination of a tubular enclosing casing of insulating material having external screw threads at an end thcr of, inetal shell having both internal and external screw threads screw-threaded onto the screw threads of said casing, :-'2 id having an end thereof retlexed over the end of said casing and into the interior of said. casing and forcibly against the inner face of said casing, said fuse having a notch therein which is formed in said shell and also in end of said casing, a fuse-hole ing' ineinloer located at the end of said casing and shell having projection whi -h is located in said notches and engages both said car-zine; and said shell and holds said shell against rotation on said casing, and an internally screw-thrcaded end cap which is screw-threaded on d shell and holds said member in the aforesaid relation.

8. In a renewable electric fuse, the combinatic i of a tubular insulating casing having a notch in the end thereof, nit ferrule on the end of said casing); having a notch which is in register with the casing no ch, and means to hold said ferrine and. easing against relative rotation including means which located i1 bol notches, and is removable fron'r said no ches by movement 9. In a renewa electric fuse, the combination of a tubular inr-nilating casing having; a notch in. the nid thereof, a metal rule on the end of said casing); having a notch which is in r 'stcr with the ca i notch. and means to hold is id ferrule and relative r-o'l'atio'a including means which catcd in hoth otcl and is removable said notches h i l of said leg, and 1P. means in said notches.

10. In a renewable electric fuse, the combi- 1 ar insulating casing having a notch in the end thereof, a metal "er-rule on the end of 7 i which is in 1 2 fusible element ovenient a7:

a t l ive rotation including a supporting incin- )Ql' for said fusible element having; a part which located in both notches, and means which retains said ineinhei said notches.

12. In a renewable electric fuse, the combination of an exte al. sa'ew threaded Fl il: 1a.: having a notch in ferrule screw thread- ;aid ailingand having: ex- Ll screw threads and a notch which is in or w h the inn notch, and .neans to .erriil w agnnust rotation on the eas- Lds including a. member which is .1 both notciies.

a renews'z to electric fuse, the coin- .:-i= of an erltiirnally screx' thrmdcd tubular insulating casin ring :1 notch in the end thereof, a :l ,le w threaded on the end of ternal screw threads a. i

inter with the cas nutch. and means to hold said c afg, rotation on the "lasing thre; ds inchulingg a lnoinber which is cres ed in both notch-es, an: w

' and having exuotch which is i i an end can s e e ied on said ferrule andv which holds said er in said notch.

. In a rencwahlo electric fuse, the combiii of an externally L row threaded tubuinsnlating' casing; having a notch in the end thereof, a metal ferrule screw tl'n'eaded on the end of said casing; and having external screw threads and a notcn which is in register with the casing notch, a, fusible element located in said casing, a supporting member for said element having a part which is located. in both of said notches and which lr'lds said ferrule against rotation on the ca sin threads, and an end can screw threadaid ferrule and which retains said sup- FRANKLIN N. CONAN l. 

